Presbyopia means, basically, "aging eyes." (Personal knowledge here

) It can easily be bad enough to produce legal blindness -- which is why so many older people have to give up driving. It can also make previous legal blindness worse.
Trifocals are a way of dealing with vision problems. They could be to correct what vision a legally blind person has left, or to deal with the problems of presbyopia, or a number of other problems.
Legal blindness deals with whether the lenses you have correct your vision, so the same prescription on one person might return them to close to 20/20 while on another person it doesn't help. So I'm not sure they could tell just by looking at the lenses whether she was legally blind.
Also, there are lens technologies that reduce thickness and weight of even very strong lenses. Again, I'm speaking from personal experience.
If JG did leave her abusive husband, it seems entirely possible that she would have moved to an area like this part of Virginia, where you can find low-paying jobs that aren't too particular about your identity and not have a lot of people paying attention to you. If her drinking problem continued, she couldn't get jobs any more, she still missed her husband...yeah.